1. Technical Field of the Invention
The present invention relates in general to telecommunications networks, and in particular, to managing signaling within telecommunications networks.
2. Description of Related Art
Signaling System no. 7 (SS7) is a signaling network separate from the voice network that is responsible for transmitting control or signaling messages pertaining to either circuit-related information (e.g., call setup, routing, teardown, etc.) or non-circuit related information (e.g., database query, network management, etc.) between signaling points. Each signaling point in the SS7 network is identified by a unique point code, which is used to route signaling messages within the SS7 network. Examples of signaling points within the SS7 network include Service Switching Points (SSPs), Signal Transfer Points (STPs) and Service Control Points (SCPs).
SSP's are associated with the telephone switches that originate, terminate and/or route calls within a telephone voice network. For example, an SSP can be a combination of a voice switch and an SS7 switch or an adjunct computer connected to the voice switch. The SSP converts signaling from the voice switch into SS7 signaling messages, which can then be sent to other SSP's through the SS7 network. All SS7 messages travel between SSP's through an STP. The STP serves as the router in the SS7 network. There are three levels of STPs: National STP, International STP and Gateway STP. National STPs exist within national SS7 networks and are capable of transferring messages to other SS7 signaling points (SSPs, STPs and SCPs) that use the same national standard of protocol. International STPs provide interconnectivity between worldwide SS7 networks using the ITU-TS protocol standard developed for SS7. Gateway STPs, often described as National Gateway STPs or Regional STPs, provide connection between carrier networks. These STPs typically perform the Gateway screening function that filter out unwanted traffic from other carrier's networks. The SCP serves as an interface to various databases that store information pertaining to call services, subscribers and networks. For example, such information can include subscriber services, call routing, calling cards, fraud protection and other relevant information.
All SS7 signaling points are interconnected via bidirectional signaling data links. Typically, there are multiple links, collectively referred to as a linkset, between two adjacent signaling points. In order to maintain a high level of reliability, links must remain available for SS7 traffic at all times, with minimal downtime. When a link fails, the other links within its linkset must accept the traffic from the failed link. However, if an entire linkset fails, alternate signaling routes must be found to redirect traffic. As is understood in the art, a “signaling route,” also known as a “routeset,” refers to the group of linksets used to reach a particular destination signaling point.
In general, the particular signaling route taken by a signaling message is determined by analyzing the origination point code (OPC) associated with the originating SSP and the destination point code (DPC) associated with the destination SSP. At each signaling point within the signaling route, the routing tables within that signaling point are accessed to determine the point code of the next signaling point to which a particular message should be routed. These routing tables are maintained by the service providers themselves and are network dependent, which allows for fault recovery and real-time re-routing of signaling messages within networks to decrease downtime.
When traffic is concentrated on a combined linkset between two pairs of STPs, a particular vulnerability occurs. If a linkset in a combined linkset begins to go in and out of service (a condition called a “bouncing linkset”), this may trigger successive waves of network management messages. The congestion caused by these messages may then result in waves of Integrated Service Digital Network (ISDN) User Part (ISUP) messages resulting from the initial outage. In order to recover from this condition, it may even become necessary to manually remove point codes from the routing database of the affected STPs in order to reduce the ISUP traffic to a level at which the linkset can recover.
However, the manual process of determining which point codes to delete from the routing database is both error prone and time consuming. In addition, when the outage is over, all of the deleted point codes must be reentered in the routing database in order to reestablish normal traffic, which again exposes the network to error and prolongs the duration of the outage. Therefore, what is needed is a method for recovery from a linkset failure at an interface between two networks that minimizes downtime of that linkset.